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Motherboard and displays

mulfycrowh , 08-16-2019, 12:46 AM
Hi everyone,
I have to design a motherboard able to run with up to 2 displays.
I have 3 devices to manage with:
1/ Device 1 with 1 display 15.6"
2/ Device 2 with 2 displays 15.6"
3/ Device 3 with 2 displays 27.0"

Each display comes with 4K Resolution, eDP port and touch screen.
Let's say that the board dimensions are about the size of 1 display 15.6".
How do I manage the connections with the displays ?
For Device 1, it's easy, but for the other ones, if you have some idea …
I fear having EMC issues if I have eDP cables running on a long distance.
The idea, maybe, would be having an interface board located near the eDP display connector and that converts the signal into HDMI ?

Thanks a lot.

mulfycrowh , 08-16-2019, 01:32 AM
I forgot also: another device (Device 4) with 1 display 27.0"
Paul van Avesaath , 08-16-2019, 05:18 AM
i am guessing that you need to switch between the two sets of monitors.. ?
so all monitors are connected and you want to send you data to one or the other..?

there are dedicated HDMI/DP switches from TI i believe.. these switch in groups of 4/8/16 and capable of doing the high speed signals.
also you can use transparent switches (these can be configured to be 4:4).. so you can have 4sets on inputs on 4 monitors and choose per signal group on which monitor its is going.. (or one source on all ,monitor at the same time..)
i have used the macom switches for SDI before they had an option to group them in that way..
but they are expensive..

a bit more info would be helpfull
mulfycrowh , 08-16-2019, 05:48 AM
Thks for reply.
When a device has 2 displays, we use them at the same time.
One is used to display a page of a pdf file, the other one the following page.
Paul van Avesaath , 08-16-2019, 06:06 AM
so would a standard ITX board with a graphics card that has 4 dp ports do the same? why a custom board?
mulfycrowh , 08-16-2019, 07:03 AM
Not possible to use standard ITX because proprietary chips and connectors. But how do you manage the cables between the displays and the motherboard?
Paul van Avesaath , 08-16-2019, 07:46 AM
you will just have 4 connectors to each monitor one cable I would assume... and make the hardware to do what you need it to do.. if you need to be able to switch you need to make a switch and or MUX to do this.. in any case I have the feeling that i am missing the context of your question.. so if you have a block schematic.. also tell what the source of the vidfeo signals will be.. your mentioning proprietary chips and connectors.. so what are they?
mulfycrowh , 08-16-2019, 09:38 AM
Each display comes with 3 cables: backlight, touch screen, display port.
How do you manage the distance between display and motherboard?
We could have 15inch, maybe more.
The cables act as antennas.
robertferanec , 08-19-2019, 02:00 AM
This looks to me more like an industrial PC with 4 graphic outputs (or a board like COM Express, PC104 etc) + your board(s) + displays. I would not be developing my own motherboard for this - that would be unnecessary expensive, risky and would take a lot of time.

Not possible to use standard ITX because proprietary chips and connectors.
What you may need is an adapter board which will have input ports like DVI, HDMI, DP and output connectors what you need. Possibly you could design a baseboard for computer on module (such COM Express).

If you are worried about EMC/EMI (I would be), maybe make number of these adapter boards (each with different interface e.g. HDMI to your special connectors, DVI to your special connectors, DP to your special connectors - depends what your industrial PC will have) and place these adapters close to the display - so for longer distance you use the standard and certified cable and interface (e.g. hdmi) and just very close to the display you use your adapter board.

Important is what your goal is:
- if to build as quickly and simply a system which has 4 monitors and can run 2 of them at the same time,
- or if your goal is to build a fully custom solution with four monitors where 2 can run at the same time, the system is neat, can not be simply copied, but cost a lot of money and can take a lot of time to develop (+ more risky to develop than the first option).
mulfycrowh , 08-19-2019, 03:37 AM
Hi Robert.
I have 2 devices.
One with one display. The other one with 2 displays.
My idea is to use COM Express board and develop a base board.
I agree with the idea about a board close to the display.
The purpose of this board would be :
- to convert the eDP port into HDMI
- to convert the touch screen signals into USB
- to generate the backlight voltage

Between this board and the base board we would have:
- shielded USB cable
- shielded HDMI cable
- shielded power supply

What do you think?
robertferanec , 08-19-2019, 05:43 AM
Ah, so you mean like you would like to use the same board in 4 different applications (each application will have 1 or 2 displays connected with different size)?
mulfycrowh , 08-19-2019, 05:47 AM
Thats right
robertferanec , 08-20-2019, 08:29 AM
Ok, I understand now. Yes, be careful about display cables - that can do a lot of mess during EMC/EMI. I am not sure how far the displays are apart and how the final system looks. You still should be fine if the cables are relatively short (e.g. 30cm) and if grounding is done properly.

If displays are further from each other, I would find a motherboard with for example two HDMI outputs and I would make an adapter board (HDMI to display) which would be placed close to display. This way, you do not need to design complex baseboard, you could design just a simple adapter board - much faster, cheaper, easier and lower risk.
mulfycrowh , 08-22-2019, 10:34 AM
Hi everyone.
I'm currently looking for a HDMI to eDP bridge?
Do you have any idea about a supplier?
Thanks a lot!
robertferanec , 08-23-2019, 07:08 AM
I have not used it before, but some may exist e.g. I googled for "hdmi to edp 4k adapter" and this is what it found:
- STDP2600 Advanced HDMI to DisplayPort converter: https://media.digikey.com/pdf/Data%2...TDP2600_DS.pdf

However I dont know much about MegaChips, maybe I would continue looking for something from more known chip manufacturer.
mulfycrowh , 08-23-2019, 07:29 AM
Hi Robert!
Not so easy to find.
You have a first approach using a first chip converting from HDMI to MIPI DSI and a second chip from MIPI DSI to eDP.
The chip SN65DSI86 (Texas Instruments) and the chip TC358870XBG (Toshiba) make it for 4K@30 fps.
I had yesterday a chat with a guy from TI and he told me they plan to develop a chip due the customers' request.

This morning I found a second and better solution (4K@60fps) with only one chip: LT6711 from Lontium Semiconductor.
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